Methods for scribing and separating strengthened glass substrates

ABSTRACT

A method of forming a scribe line in a strengthened glass substrate includes providing a strengthened glass substrate having a first surface, a second surface, a first edge and a second edge. The first and second surfaces have a strengthened surface layer under a compressive stress, and a central region under tensile stress. The method further includes applying a scoring blade to the first surface at an initiation location that is offset from the first edge by an initiation offset distance greater than a diameter of the scoring blade, and translating the scoring blade or the strengthened glass substrate such that the scoring blade scores the first surface. The translation is terminated such that the scoring blade stops at a termination location that is offset from the second edge of the strengthened glass substrate by a termination offset distance greater than the diameter of the scoring blade.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/364,980 filed on Jul. 16, 2010the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

1. Field

The present specification generally relates to methods for separatingglass substrates and, more specifically, to methods for scribing andseparating strengthened glass substrates.

2. Technical Background

Thin glass substrates have a variety of applications in consumerelectronic devices. For example, glass substrates may be used as coversheets for LCD and LED displays incorporated in mobile telephones,display devices such as televisions and computer monitors, and variousother electronic devices. Cover sheets used in such devices may beformed by sectioning or separating a large glass substrate into aplurality of smaller glass substrates. For example, glass substrates maybe separated by scribe-and-break techniques. However, whenscribe-and-break techniques are utilized to separate strengthened glass,such as ion-exchanged glass, uncontrollable full-body separation orshattering may occur rather than the formation of a scribe line. Theuncontrolled separation generally leads to poor edge characteristics orcomplete destruction of the glass substrate. Further, the scoring deviceused to score the strengthened glass may not be able to penetrate thecompressive surface of the strengthened glass, thereby preventing theformation of a scribe line.

Accordingly, a need exists for alternative methods for forming scribelines and separating strengthened glass substrates.

SUMMARY

In one embodiment, a method of forming a scribe line in a strengthenedglass substrate includes providing a strengthened glass substrate havinga first surface, a second surface, a first edge and a second edge. Eachof the first and second surfaces has a strengthened surface layer undera compressive stress and extending from the surface to a depth of layer,and a central region between the first and second surfaces under tensilestress. The method further includes applying a scoring blade to thefirst surface at an initiation location that is offset from the firstedge by an initiation offset distance that is greater than a diameter ofthe scoring blade, and translating the scoring blade or the strengthenedglass substrate such that the scoring blade scores the first surfacealong a desired line of separation. The translation of the scoring bladeor the strengthened glass substrate is terminated such that the scoringblade stops at a termination location that is offset from the secondedge of the strengthened glass substrate by a termination offsetdistance that is greater than the diameter of the scoring blade.

In another embodiment, a method of separating a strengthened glasssubstrate includes providing the strengthened glass substrate, whereinthe strengthened glass substrate has a first surface, a second surface,a first edge and a second edge. Each of the first surface and the secondsurface has a strengthened surface layer under a compressive stress andextending from the surface to a depth of layer, and a central regionbetween the first surface and the second surface that is under tensilestress. The method further includes applying a scoring blade to thefirst surface at an initiation location such that the initiationlocation is offset from the first edge by an initiation offset distancethat is greater than a diameter of the scoring blade, and translatingthe scoring blade or the strengthened glass substrate such that thescoring blade scores the first surface along a desired line ofseparation, thereby forming a scribe line. The translation of thescoring blade or the strengthened glass substrate is terminated suchthat the scoring blade stops at a termination location that is offsetfrom the second edge of the strengthened glass substrate by atermination offset distance that is greater than the diameter of thescoring blade. The method further includes applying a bending momentabout the scribe line to controllably break the strengthened glasssubstrate along the scribe line, thereby separating the strengthenedglass substrate.

In yet another embodiment, a strengthened glass article includes a firstsurface, a second surface, and at least one edge joining the first andsecond surfaces. Each of the first surface and the second surface has anion exchanged strengthened surface layer under a compressive stress andextending from the surface to a depth of layer, and a central regionbetween the first surface and the second surface that is under tensilestress. The at least one edge is formed by applying a scoring blade to afirst surface of a strengthened glass substrate at an initiationlocation that is offset from the first edge of the strengthened glasssubstrate by an initiation offset distance that is greater than adiameter of the scoring blade, translating the scoring blade or thestrengthened glass substrate such that the scoring blade scores thefirst surface along a desired line of separation, terminating thetranslation of the scoring blade or the strengthened glass substratesuch that the scoring blade stops at a termination location that isoffset from a second edge of the strengthened glass substrate by atermination offset distance that is greater about than the diameter ofthe scoring blade, and applying a bending moment about the scribe lineto controllably break the strengthened glass substrate along the scribeline, thereby separating the strengthened glass substrate.

Additional features and advantages of the methods will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the embodiments described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

FIG. 1 schematically depicts a cross sectional view of a chemicallystrengthened glass substrate according to one or more embodimentsdescribed and illustrated herein;

FIG. 2 graphically depicts compressive and tensile stresses within achemically strengthened glass substrate according to one or moreembodiments described and illustrated herein;

FIG. 3 schematically depicts a top view of a chemically strengthenedglass substrate being scribed according to one or more embodimentsdescribed and illustrated herein;

FIG. 4 schematically depicts a scoring blade according to one or moreembodiments described and illustrated herein; and

FIG. 5 schematically depicts a perspective view of two separatedchemically strengthened glass articles according to one or moreembodiments described and illustrated herein.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of methodsfor forming scribe lines in strengthened glass substrates and separatingstrengthened glass substrates by the formation of scribe lines. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts. As described herein,methods for forming a scribe line in a strengthened glass substrategenerally comprise applying a scoring blade to a first surface (e.g., atop surface) at an initiation location that is offset from a first edgeof strengthened glass substrate. The scoring angle of the scoring blade,as well as the force applied to the strengthened glass substrate, aresuch that a scribe line created by the application of the scoring bladedoes not extend too deeply into a central region under tensile stress.The scoring blade or the glass substrate is translated such that thescoring blade scores the first surface, thereby forming the scribe line.The translation may be terminated prior to the scoring blade reaching asecond edge of the strengthened glass substrate. The strengthened glasssubstrate may be separated by the application of a mechanical forceabout the formed scribe line. Various embodiments of the methods forforming scribe lines in strengthened glass substrates, methods for theseparation of strengthened glass substrates, and strengthened glassarticles will be described in more detail herein.

Referring to FIG. 1, an exemplary strengthened glass substrate 100 isillustrated. The strengthened glass substrate 100 has a first surface110 a, a second surface 110 b, and edges (e.g., a first edge 111 and asecond edge 113). The strengthened glass substrate 100 may be chemicallystrengthened by an ion-exchange process to produce strengthened surfacelayers 112 a, 112 b and a central region 114 within the glass substrate.The glass substrate may be formed from various glass compositionsincluding, without limitation, soda lime silicate glasses, borosilicateglasses, aluminosilicate glasses, and aluminoborosilicate glasses,including ion-exchanged borosilicate, aluminosilicate glasses, andaluminoborosilicate glasses. As an example and not a limitation, theglass substrate may be Corning Gorilla® glass.

The strengthened glass substrate 100 comprises two strengthened surfacelayers 112 a and 112 b, and a central region 114. The strengthenedsurface layers 112 a and 112 b are kept in a compressive stress statethat provides the strengthened glass substrate 100 its high strength.The central region 114 is under tensile stress to compensate for thecompressive stresses in the strengthened surface layers 112 a and 112 bsuch that the forces balance each other and the strengthened glasssubstrate 100 does not fracture. FIG. 2 graphically illustrates a stressprofile of an exemplary strengthened glass substrate 100. The twostrengthened surface layers 112 a and 112 b have an ion-exchange depthof layer (DOL) as indicated by depth 136. The DOL in some embodimentsmay be greater than 1/30^(th) of the total thickness of the strengthenedglass substrate.

Graph lines 132 a, 132 b, and 132 c illustrate the stress profile indifferent regions of the glass substrate. Line 134 represents zerostress forces and arrow 130 represents increasing/decreasing compressiveand tensile stresses. As illustrated in FIG. 2, the stress profile inthe strengthened surface layers 112 a and 112 b of the exemplarystrengthened glass substrate 100 are under significant compressivestress (e.g., about 600 MPa or more near the surface of the strengthenedglass substrate 100). The center tension of the inner tension regionincreases as a reaction to the increase of compressive surface stress(e.g., up to about 45 MPa in one embodiment). In general, the magnitudeof central tension stress impacts the glass fragmentation and themagnitude of surface compressive stress determines the strength of theglass substrate.

Embodiments described herein utilize a scoring blade to mechanicallyform a scribe line by applying and translating the scoring blade acrossa surface of the strengthened glass substrate 100. FIG. 3 schematicallydepicts a strengthened glass substrate 100 and a scoring blade 120applied thereto. The strengthened glass substrate 100 may be placed in acomputer-controlled X, Y bridge machine (not shown). The bridge machinemay control the movement of the scoring blade 120 along a desired lineof separation 116. The desired line of separation 116 is the line onwhich the scoring blade is translated and the scribe line is formed. Thestrengthened glass substrate 100 may then be separated by mechanicalforce at the scribe line after the scribing process. In anotherembodiment, the scoring blade 120 may remain static and the strengthenedglass substrate 100 may be mounted on a translation table thattranslates the strengthened glass substrate 100 with respect to thescoring blade 120.

The scoring blade 120 may be applied to a first surface 110 a of thestrengthened glass substrate at an initiation location 115. It should beunderstood that the scoring blade 120 may also be applied to the secondsurface 110 b. The scoring blade 120 may be any type of blade used toscore glass. For example, the scoring blade 120 may be a scoring wheel,as illustrated in FIG. 4. However, the shape of the scoring blade 120 isnot limited to a circular wheel and may have other configurations (e.g.,rectangular). The scoring blade 120 may be made of materials such astungsten carbide or diamond polycrystalline, for example.

As illustrated in FIG. 4, the scoring blade 120 may have angled walls122 that define a scoring angle θ and a scribing edge 124. The scoringangle θ should be such that the scribing blade may effectively cut intothe strengthened glass substrate without causing shattering or full-bodyseparation. Too sharp of a scoring blade 120 may create a surfacedefect/scribe line that enters too deeply into the central region 114under tensile stress and cause a full-body separation or shattering ofthe strengthened glass substrate. A scoring blade that is too dull maynot be able to penetrate the strengthened surface layer to form asurface defect. In one embodiment, the scoring angle θ illustrated inFIG. 4 may be between about 100° and about 130° to form a surface defect125 into the strengthened glass substrate 100 that does not extend toodeeply into the central region 114.

The diameter d of the scoring blade 120 should be relatively small.Large diameter scoring blades may create uncontrollable cracks in thestrengthened glass substrate 100. Although larger diameter scoringblades may be utilized, scoring blades having a diameter d that is lessthen or equal to 5 mm may consistently form a scribe line in thestrengthened glass substrate 100.

The application of the scoring blade 120 on the surface 110 a/110 bcreates a surface defect 125 at the impact location (FIG. 1).Microscopic evaluation of surface defects formed on the surface ofstrengthened glass substrates indicates that surface defects created atthe impact location extend from the impact location toward both the edgeclosest to the impact location (e.g., first edge 111) and the oppositeedge (e.g., second edge 113). The average length of the surface defect125 created by the application of the scoring blade was measured to beabout 1.5 times the diameter d of the scoring blade 120. The length ofthe surface defect 125 may be longer at the initiation location 115 thanother locations along the desired line of separation 116, including thetermination location 117. The initial impact of the scoring blade 120 onthe strengthened glass substrate 100 may result in a transient increaseof impact force at the initiation location such that a length of thesurface defect 125 is greater at the impact location than otherlocations along the desired line of separation 116.

Applying the scoring blade 120 at an edge, or close to an edge, of astrengthened glass substrate during the scribing process may cause thesurface defect 125 to reach the edge, and allow multiple cracks/vents toform within the strengthened glass substrate 100, which mayuncontrollably veer from the desired line of separation or causefull-body separation or the strengthened glass substrate 100 to shatter.A single crack or vent following the desired line of separation 116 mayenable the strengthened glass substrate 100 to be separated cleanly withsmooth edges.

To prevent the formation of multiple, uncontrollable cracks, the scoringblade 120 may be applied to the first surface 110 a of the strengthenedglass substrate 100 at an initiation location 115 that is offset fromthe first edge 111 by an initiation distance D_(I). The initiationdistance D_(I) should be large enough such that surface defect 125radiating from the initiation location 115 toward the first edge 111does not reach the first edge 111. Generally, the initiation distanceD_(I) should be greater than the diameter d of the scoring blade.Applying the scoring blade 120 at an initiation location that is offsetfrom the first edge 111 by an initiation distance D_(I) may prevent anopen crack or cracks from forming and reaching the central region 114 ofthe strengthened glass substrate 100. If the initiation location 115 ispositioned too close to the first edge 111 of the strengthened glasssubstrate 100, the surface defect 125 may reach the first edge 111 andcause the surface defect 125 to enter the central region 114 at orproximate the first edge 111 and form an open crack. In one embodiment,the initiation distance D_(I) is at least two times the diameter d ofthe scoring blade 120, which may prevent the surface defect 125 createdat the initiation location 115 from reaching the first edge 111.

The impact energy of the scoring blade 120 on the first surface 110 a,both at initial impact and during translation, should be controllablymaintained such that the surface defect 125 (and subsequently formedscribe line) does not extend too deeply into the central region 114 ofthe strengthened glass substrate 100. As illustrated in FIG. 1, thesurface defect 125 may extend partially into the central region 114under tensile stress. However, the strengthened glass substrate 100 maybe sufficiently rigid to prevent full-body separation when the surfacedefect 125 minimally enters the central region 114. If the surfacedefect 125 enters too deeply into the central region 114, full-bodyseparation or shattering may occur.

Generally, the impact energy of the scoring blade 120 on the firstsurface 110 a should be such that a depth of the surface defect 125 andresulting scribe line is not greater than about twenty-five percent ofthe total thickness of the strengthened glass substrate 100. This mayensure that the majority of the surface defect 125 and scribe line ismaintained mostly within the strengthened surface layers 112 a or 112 b.The impact energy is determined by the impact load of the scoring bladeon the strengthened glass substrate as well as both the impact speed ofthe scoring blade upon initial impact on the strengthened glasssubstrate and the translation speed of the scoring blade during thescoring operation.

Regarding initial impact of the scoring blade on the strengthened glasssubstrate, as the impact force or load increases, the impact speed ofthe scoring blade on the strengthened glass substrate should decrease.As the impact speed increases, the impact force or load should decrease.For a fixed applied load, the impact energy increases with an increaseof impact speed. Therefore, for a fixed applied load, the impact speedshould be set such that the surface defect does not extend too deeplyinto the central region of the strengthened glass substrate (e.g.,extending more than 25% of the total thickness of the strengthened glasssubstrate). The force and speed values of the scoring blade at initialimpact may depend on characteristics of the strengthened glasssubstrate, such as glass composition, thickness, the compressivestresses, and DOL of the strengthened surface layers. Table 1illustrates three strengthened glass substrates of different thicknesseshaving a tensile stress of 30 MPa in the central region and the maximumspeed and impact force values resulting from experimental testing. Table2 illustrates three strengthened glass substrates of differentthicknesses having a tensile stress of 22 MPa in the central region andthe maximum speed and impact force values resulting from experimentaltesting. It should be understood that the values listed in Tables 1 and2 are for illustrative purposes only and are not intended aslimitations.

TABLE 1 Strengthened Glass Substrate Having 30 MPa Central Region GlassThickness Impact Speed Applied Load 1.1 mm 125 mm/s 18N 0.7 mm 100 mm/s16N 0.55 mm   75 mm/s 14N

TABLE 2 Strengthened Glass Substrate Having 22 MPa Central Region GlassThickness Impact Speed Applied Load 1.1 mm 100 mm/s  18N 0.7 mm 90 mm/s16N 0.55 mm  50 mm/s 14N

Regarding impact energy during the translation of the scoring blade onthe surface of the strengthened glass substrate, an increase of scoringspeed of the scoring blade (i.e., translation speed) may necessitate acorresponding increase in applied force of the scoring blade on thesurface on the strengthened glass substrate. As a general rule, a 50%increase in translation speed of the scoring blade 120 may necessitate a15% increase in impact force to achieve a scribe line having a properdepth to enable separation of the strengthened glass substrate.Successful scribe line generation was performed at scribing speedsbetween 10 mm/s and 1000 mm/s. Table 3 illustrates scribing cracks ofvarious depths resulting from different translation speeds andcorresponding impact forces in 0.7 mm thick ion exchanged glass sampleshaving a central tension region of 30 MPa. It should be understood thathe values provided in Table 3 are illustrative and non-limiting.

TABLE 3 Scoring Speed and Scoring Force - 0.7 mm Thick CT-30 Glass LoadScoring Speed Median Crack Depth 12N 250 mm 109.5 μm 12N 500 mm 100 μm15N 250 mm 117 μm 15N 500 mm 109.5 μm 18N 250 mm 125.5 μm 18N 500 mm 111μm

In one embodiment, the force and speed of impact and translation of thescoring blade 120 on the first surface 110 a of the strengthened glasssubstrate 100 is controlled by the use of a controllable pneumaticcylinder. The force may be controlled by a pressure valve of thepneumatic cylinder, and the impact speed on the first surface 110 a maybe controlled by controlling the flow rate of the pneumatic cylinder.Other methods of controlling the force and speed of the scoring blademay also be utilized, such as by the use of servo motors and hydrauliccylinders.

Referring once again to FIG. 3, the scoring blade 120 or thestrengthened glass substrate is translated such that the scoring blade120 traverses the first surface 110 a of the strengthened glasssubstrate 100 along the desired line of separation 116 in direction A,thereby forming a scribe line that closely follows the desired line ofseparation 116. The X, Y bridge machine or translation table may becomputer-controlled to translate the scoring blade 120 along the desiredline of separation. The translation may be driven by one or more servomotors of the X, Y bridge machine or translation table.

As shown in FIG. 3, the scoring blade 120 may be stopped at atermination location 117 that is offset from the second edge 113 by atermination distance D_(T). The termination distance D_(T) should belarge enough such that the scribe line does not extend past the finalimpact location of the scoring blade 120 to reach the second edge 113.The termination distance D_(T) should be greater than the diameter d ofthe scoring blade. An uncontrollable crack or full-body separation mayoccur if the surface defect 125 reaches the second edge 113. Asdescribed above with respect to the initiation location 115, an opencrack may form at or proximate to the second edge 113 if the surfacedefect 125 reaches the second edge 113 because the surface defect mayextend into the central region 114. In one embodiment, the terminationdistance D_(T) is at least about 1.5 times the diameter d of the scoringblade 120.

After forming a scribe line as described above, the strengthened glasssubstrate 100 may be separated into strengthened glass articles byapplying a force about the scribe line. The force may be mechanicallyapplied by a bending machine configured to apply a bending moment aboutthe scribe line. The force may also be applied by pushing or pullingregions of the strengthened glass substrate such that a crack opensalong the scribe line to separate the strengthened glass articles fromthe strengthened glass substrate. Any number of methods for applying amechanical force to separate the strengthened glass substrate may beutilized.

FIG. 5 illustrates two strengthened glass articles 140 and 142 that wereseparated from a strengthened glass substrate utilizing the methodsdescribed herein. The first and second strengthened glass articles 140,142 have edges 119 a and 119 b, respectively, which were formed by firstmechanically scoring a scribe line onto a surface of a strengthenedglass substrate as described above. Following the formation of thescribe line, a mechanical force is applied to the strengthened glasssubstrate at the scribe line to controllably break the strengthenedglass substrate into two strengthened glass articles 140, 142. Anynumber of strengthened glass articles may be separated from thestrengthened glass substrate. The controlled force initiates a full bodycrack through the strengthened glass substrate 100 through the scribeline such that the strengthened glass articles have a predeterminededge.

As an example and not a limitation, a 0.7 mm thick ion-exchangedstrengthened glass substrate having a 30 MPa center region, strengthenedsurface layers of 750 MPa, and a DOL of 27 μm, was separated using themethods described above. A 100° angle, 2 mm diameter scoring wheel wastranslated on the strengthened glass substrate at a rate of 500 mm/s anda scoring load of 18N to score the scribing line. The scoring wheel wasapplied at an initiation location that was offset from a first edge byabout 5 mm The translation of the scoring wheel was stopped at atermination location that was offset from a second edge (opposite fromthe first edge) by about 4 mm The scribe line was formed withoutfull-body separation or uncontrollable cracks or vents. The strengthenedglass substrate was then separated by mechanical force about the scribeline.

It should now be understood that the methods described herein may beused to separate strengthened glass substrates, such as strengthenedglass substrates made from borosilicate glasses, aluminosilicateglasses, and aluminoborosilicate glasses. Methods described herein mayenable strengthened glass substrates to be separated by ascribe-and-break process, wherein a scribe line is mechanically formedby the application of a scribing blade. The formed scribe line does notcontact an edge of the glass substrate, thereby preventing shatteringdue to impact of the scribing blade on a glass edge, spontaneousseparation of the strengthened glass substrate due to a free crack undertension stress, and shattering due to impact defect. Strengthened glasssubstrates having scribe lines described herein may be separated by anapplication of force to the strengthened glass substrate along thescribe line to produce strengthened glass articles.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments describedherein, provided such modification and variations come within the scopeof the appended claims and their equivalents.

1. A method of forming a scribe line in a strengthened glass substrate,the method comprising: providing the strengthened glass substrate, thestrengthened glass substrate comprising a first surface, a secondsurface, a first edge and a second edge, wherein each of the firstsurface and the second surface has a strengthened surface layer under acompressive stress and extending from the surface to a depth of layer,and a central region between the first surface and the second surfacethat is under tensile stress; applying a scoring blade to the firstsurface at an initiation location, wherein the initiation location isoffset from the first edge by an initiation offset distance that isgreater than a diameter of the scoring blade; translating the scoringblade or the strengthened glass substrate such that the scoring bladescores the first surface along a desired line of separation; andterminating the translation of the scoring blade or the strengthenedglass substrate such that the scoring blade stops at a terminationlocation that is offset from the second edge of the strengthened glasssubstrate by a termination offset distance that is greater than thediameter of the scoring blade.
 2. The method of claim 1, wherein theinitiation offset distance is at least two times the diameter of thescoring blade.
 3. The method of claim 1, wherein the termination offsetdistance is at least one and a half times greater than the diameter ofthe scoring blade.
 4. The method of claim 1, wherein an impact energyapplied to the first surface by the scoring blade is such that thescribe line has a depth that is less than twenty-five percent of a totalthickness of the strengthened glass substrate.
 5. The method of claim 1,wherein an impact energy applied to the first surface by the scoringblade is between 15N and 19N.
 6. The method of claim 1, wherein atranslation speed of the scoring blade or the strengthened glasssubstrate is greater than 10 mm/s.
 7. The method of claim 1, wherein thediameter of the scoring blade is between 2 mm and 3 mm
 8. The method ofclaim 1, wherein a scoring angle of the scoring blade is between 100°and 130°.
 9. The method of claim 1, wherein the strengthened surfacelayers have a compressive stress that is greater than 600 MPa, and athickness that is greater than 1/30th of a thickness of the strengthenedglass substrate.
 10. A method of separating a strengthened glasssubstrate, the method comprising: providing the strengthened glasssubstrate, the strengthened glass substrate comprising a first surface,a second surface, a first edge and a second edge, wherein each of thefirst surface and the second surface has a strengthened surface layerunder a compressive stress and extending from the surface to a depth oflayer, and a central region between the first surface and the secondsurface that is under tensile stress; applying a scoring blade to thefirst surface at an initiation location, wherein the initiation locationis offset from the first edge by an initiation offset distance that isgreater than a diameter of the scoring blade; translating the scoringblade or the strengthened glass substrate such that the scoring bladescores the first surface along a desired line of separation, therebyforming a scribe line; terminating the translation of the scoring bladeor the strengthened glass substrate such that the scoring blade stops ata termination location that is offset from the second edge of thestrengthened glass substrate by a termination offset distance that isgreater than the diameter of the scoring blade; and applying a bendingmoment about the scribe line to controllably break the strengthenedglass substrate along the scribe line, thereby separating thestrengthened glass substrate.
 11. The method of claim 10, wherein: theinitiation offset distance is at least two times the diameter of thescoring blade; and the termination offset distance is at least one and ahalf times greater than the diameter of the scoring blade.
 12. Themethod of claim 10, wherein an impact energy applied to the firstsurface by the scoring blade is such that the scribe line has a depththat is less than twenty-five percent of a total thickness of thestrengthened glass substrate.
 13. The method of claim 10, wherein ascoring load applied to the first surface by the scoring blade isbetween 15N and 19N.
 14. The method of claim 10, wherein a translationspeed of the scoring blade or the strengthened glass substrate isgreater than 10 mm/s.
 15. The method of claim 10, wherein the diameterof the scoring blade is between 2 mm and 3 mm, and a scoring angle ofthe scoring blade is between 100° and 130°.
 16. The method of claim 10,wherein the strengthened surface layers have a compressive stress thatis greater than 600 MPa, and a thickness that is greater than 1/30th ofa thickness of the strengthened glass substrate.
 17. A method of forminga scribe line in a strengthened glass substrate, the method comprising:providing the strengthened glass substrate, the strengthened glasssubstrate comprising a first surface, a second surface, a first edge anda second edge, wherein each of the first surface and the second surfacehas a strengthened surface layer under a compressive stress andextending from the surface to a depth of layer, and a central regionbetween the first surface and the second surface that is under tensilestress; applying a scoring blade to the first surface at an initiationlocation with a scoring load between 15N and 19N and an impact speedbetween 75 mm/s and 125 mm/s, wherein the initiation location is offsetfrom the first edge by an initiation offset distance that is greaterthan two times a diameter of the scoring blade; translating the scoringblade or the strengthened glass substrate at a scoring speed between 100mm/s and 500 mm/s such that the scoring blade scores the first surfacealong a desired line of separation and at a depth of less thantwenty-five percent of a total thickness of the strengthened glasssubstrate; and terminating the translation of the scoring blade or thestrengthened glass substrate such that the scoring blade stops at atermination location that is offset from the second edge of thestrengthened glass substrate by a termination offset distance that isgreater than one and a half times the diameter of the scoring blade. 18.The method of claim 17, wherein the total thickness of the strengthenedis between 0.55 mm and 1.1 mm, and the tensile stress is between 20 MPaand 45 MPa.
 19. The method of claim 17, wherein the diameter of thescoring blade is between 2 mm and 3 mm, and a scoring angle of thescoring blade is between 100° and 130°.
 20. The method of claim 17,wherein the strengthened surface layers have a compressive stress thatis greater than 600 MPa, and a thickness that is greater than 1/30th ofa thickness of the strengthened glass substrate.